A variety of devices are conventionally used to treat bone fractures. Intramedullary nail systems (also known as intramedullary rod systems) are employed in orthopedic surgery for repairing fractures of long bones, such as the femur and humerus. Use of intramedullary nail systems reduces healing time, permits less immobilization of the affected limb, and simplifies treatment of complex fractures.
An example of a conventional intramedullary nail used for humeral repair generally takes the form of an elongated cannulated body. At various locations along its length, the nail is provided with one or more transverse openings for receiving screws. Typically, at least one transverse opening is located near an end of the nail. The openings are commonly adapted to receive the screws at various angles in order to repair a wide range of fractures in a variety of patients using the same nail design. The nail is normally provided with a securing arrangement on at least one end. The securing arrangement is for securing a tool or device for inserting and extracting the nail, as well as maintaining the nail's desired position during insertion. In order to facilitate correct insertion of the nail into a medullary canal, various guiding devices and arrangements are used. Examples of such arrangement are guiding wires, sleeves, or pins.
To repair a bone fracture using an intramedullary nail system, a medullary canal of the bone is reamed using an appropriate tool or device. An intramedullary nail is inserted into the medullary canal and advanced axially through the canal so that the nail traverses the fracture site. Then, one or more screws or pins are applied to the nail through the transverse openings in the nail. The screws extend through the bone on one or both sides of the fracture site so that the nail is attached to portions of the bone on each side of the fracture, thereby securing the bone segments and allowing healing along the fracture site.
One of the problems commonly associated with the intramedullary nail systems is insufficient retention of the screws or pins in the nail, which causes undesirable movement in the system. Detrimental to healing consequences of such undesirable movement include but are not limited to, the fracture becoming unreduced, collapse of parts of the bone onto each other, or damage to bones or soft tissues by bone parts or parts of the system.
Intramedullary nail systems are commonly designed to allow insertion of the screws or pins in the nail at various angles. In one aspect, this feature ensures an ability to use the same nail to repair various fractures in bones in a range of sizes and shapes. This eliminates the necessity to have available different types of intramedullary nail systems, each allowing insertion of screws at specific angles. In another aspect, the ability to vary the angle of insertion of a screw into an opening in the nail allows to compensate for misalignments that occur during surgery.
There are, however, problems associated with the openings capable of receiving screws at a range of angles. Particularly, this feature leads to wobbling of the end of the screw inserted in the nail. For stabilization, the screw relies on purchase of its other end to the bone tissue. The undesirable movement occurs if the purchase to the bone tissue is inadequate, or is lost after the reduction of the fracture. Moreover, wobbling of the end of the screw inserted in the nail increases the tension applied by the other end of the nail to the bone tissue and may facilitate the destruction of the bone tissue.
Long bones such as femur and humerus can be fractured in the lower portion, the mid portion or the upper portion, where the bone connects to the joint. The third scenario is typically referred to as a proximal fracture. Proximal fractures of long bones, such as femur or humerus, frequently occur in women with osteoporosis, a condition of brittle, fragile bones. Osteoporosis is highly prevalent in women, especially in those post menopause, thus making repair of the proximal fractures of femur and humerus an important public health issue.
The repair of proximal humeral fractures using intramedullary nails is especially difficult. In proximal humerus, the bone is mostly cancellous and of relatively low density. Due to poor bone quality, adequate stabilization of the humeral head or tuberosities during bone fracture repair is challenging and is not provided by currently available intramedullary nail systems and techniques.
Traditional humeral nails use one or two proximal screws for fixation. To reduce a fracture, these constructs rely on purchase of screw threads to the bone in order to hold the fragments of the bone together. When the thread purchase in the bone is lost, the fracture becomes unreduced. Additionally, the loose screws cause damage to the surrounding bone and the soft tissues.
Other currently available nails for repair of proximal humeral fractures use multiple non-coplanar screws for proximal fixation. These designs are less dependent upon thread purchase due to the use of diverging or converging fixation pattern. By having two non-coplanar screws attached to a single bone fragment, the pullout forces are directed away from axes of each the screws. These constructs rely on fixation of the screws to bone tissue, which can lead to the deterioration of the bone tissue.
Both types of constructs described above require sufficient amount and quality of bone tissue for fixation of the fracture. When the bone tissue is lost due to disease or a pathological condition or for other reasons, the constructs become unstable. Persons with thin or fragile bones, such as osteoporosis patients, avascular necrosis patients and patients with metastatic bones, are particularly prone to fractures. Therefore, currently available intramedullary nail systems do not satisfy the requirements of the patients who are in particular need of such constructs.
In view of the foregoing, there is a need for intramedullary nail systems which provide increased stabilization of screws in an intramedullary nail, while simultaneously allowing insertion of the screws into the nail at a range of angles. There is also a need for intramedullary nail systems which reduce undesirable movement in a bone fracture stabilized with the system, and reduce undesirable movement of the components of the system with respect to each other. Ability of an intramedullary nail system to reduce the fractures of bones of poor quality, such as those occurring during osteoporosis, cancer or other pathological conditions, is also desirable. In general, there is a need for intramedullary nail systems which are versatile, allow for faster healing with fewer complications, require less immobilization, are easy to use and manufacture, and are less costly to produce and operate.